The objectives of the study are to assess the effects of phenobarbital, a commonly prescribed anti~convulsant, on tests of intelligence and behavior in children. The design of this study permitted com~parison of measures of tested intelligence and of behavior in children with febrile seizures who had been treated with phenobarbital, and in a group of seizure~free control children. A comparison of the groups allowed assessment of benefit and risk of treatment for a common childhood neurologic problem.